Research compilers are mostly not robust or complete enough to handle real, large applications. They are used mostly for fast prototyping new language features and new optimizations in research areas.

Open64: one of the most popular research compilers today, many branches exist. Here is a list of research papers from the CGO 2009. Open64 merges the open source changes from the PathScale compiler mentioned.

MILEPOST GCC: interactive plugin-based open-source research compiler that combines the strength of GCC and the flexibility of the common Interactive Compilation Interface that transforms production compilers into interactive research toolsets.

Interactive Compilation Interface - a plugin system with high-level API to transform production-quality compilers such as GCC into powerful and stable research infrastructure while avoiding developing new research compilers from scratch